Re: John Hurt is off the list!
Let's not forget the name of the Valeyard was also mentioned, as in an incarnation of the doctor. Perhaps that was John Hurt.....after all, he didn't use the name "The Doctor", using Valeyard which apparently means "learned court prosecutor".
Besides, the regeneration limit was easily circumvented by the Master - he'd finished his regenerations and looked like a turd wrapped in bandages for a couple of series (Deadly Assassin?).